import java.util.Iterator;

/**
 * Created by zhangyunqi on 2017/9/22.
 */
public class BagInterface {
    class Bag<Item> implements Iterable <Item> {
        private int N;
        private Node <Item> first;

        @Override
        public Iterator <Item> iterator() {
            return null;
        }

        private class Node<Item> {
            private Item item;
            private Node <Item> next;

        }
    }
}